GlaxoSmithKline (NYSE: GSK) will pay $99 million to take full control of Cellzome, a closely held company, to boost its drug discovery efforts, the drug giant said Tuesday.

The purchase isn’t subject to regulatory approvals and will probably close on May 21, London-based Glaxo said today in a statement.

Glaxo already owned a 20 percent stake in Cellzome and had collaborated with the company for four years.

Cellzome, which has laboratories in Cambridge, England, and Heidelberg, Germany, developed technologies that will help Glaxo observe how experimental medicines interact with both intended and unintended targets in the body and may allow the company to identify safety issues earlier in the drug discovery process, Glaxo said.

“The acquisition of Cellzome adds significantly to our scientific capabilities and capacity to characterize drug targets and provides the opportunity to further enhance GSK’s ability to bring medicines to patients in a more effective manner,” John Baldoni, senior vice president of Glaxo’s platform and technology science division, said in the statement.

Glaxo noted that the deal is its third “platform technology acquisition” in the past five years, giving it more “expertise in the scientific platforms upon which new medicines are discovered, developed and readied for manufacture.”

GSK acquired Domantis for next generation of antibody therapies, and Praecis, a Massachusetts-based company focused on “novel therapeutic programs and an innovative chemical-synthesis and screening technology” in 2007.

Cellzome, founded in 2000, employs about 100 people and also has partnerships with drugmakers Johnson & Johnson and Novartis AG. Cellzome investors include Advent International, Atlas Venture, Astellas Venture Capital, Biofrontier Partners, Heidelberg Innovation, Index Ventures, Invesco Private Capital, SV Life Sciences, SG Asset Management and Sofinnova Partners.

“We are pleased to announce this transaction, which will enable GSK to progress the technologies that we have been developing for more than a decade,” said Tim Edwards, chief executive officer of Cellzome. “This follows nearly four years of successful collaboration with GSK, during which time we demonstrated the value and breadth of the Cellzome platform for drug discovery.”

Cellzome’s shareholders plan to spin off a separate company that would hold the rights to certain Cellzome assets and activities that Glaxo doesn’t want to pursue, Glaxo said.

Glaxo, the U.K.’s biggest drugmaker which operates its U.S. headquarters in RTP, has been seeking to expand existing partnerships recently. The company this month started a $2.6 billion hostile takeover bid for Human Genome Sciences Inc., its U.S. partner on the Benlysta lupus treatment.

Earlier this year, Glaxo also raised its stake in Theravance Inc., with which it is collaborating on experimental respiratory drugs.

(Bloomberg news contributed to this report.)

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